a) Field of the invention
This invention relates to an acid solution for removing zinc on the surface and in the pores of a galvanized metal (especially a galvanized steel) part. The invention also relates to a method for removing zinc on the surface and in the pores of a galvanized metal (especially a galvanized steel) part for the purpose of recycling and reusing said part.
b) Description of the prior art
Multiple etching solutions exist to clean surfaces of metal or take off the zinc coating on steel. However, etching takes place in strong acid or basic conditions that may be harmful to the user. Also, as sand-blasting will do, the integrity of the surface of the metal is affected by the acid or alkaline solution which may cause embrittlement or blistering. For recycling purposes, embrittlement or blistering must be avoided to ensure integrity (i.e. strength) of the structure to be cleaned.
Japanese patent application 84-211,576 discloses a solution of strong alkali to remove Zn coating film before soldering. However, the operation must be done on the exact site of the removal because the solution injures the metal surface.
Japanese patent application 84-009,174 discloses a solution that partially removes Zn coating film The solution comprises a high concentration of sulphuric acid that may alter the integrity of the metal surface and cause hydrogen embrittlement.
German patent 3,047,088 discloses a method for removing zinc from metal strips comprising an acid treatment followed by neutralization with an alkaline solution. Once again, this procedure involves use of very strong acid solutions that may present danger for the user. Furthermore, the acid must be neutralized before the cleaned part can be used.
Japanese patent application 77-022,331 discloses a bath for removing a Zn coating formed on steel surfaces, this solution comprising persulfate, organic complexing agents such a citric acid, EDTA or tartaric acid.
U.S. Pat. No. 3,634,217 discloses a solution for removing previously defined amounts of metal from a metal surface. The solution consists of aqueous alkaline solution and chelateforming agents.
French patent 2,029,321 discloses a cleaning solution comprising 15-33% by wt. of phosphoric acid and corrosion inhibitors such as aldehydes or urea derivatives.
It has now been found that an acid solution in admixture with a wetting agent and an inhibitor can be a very efficient solution for removing zinc coating on galvanized metal (especially a galvanized steel) parts both on the outer surface and in the pores of the metal. This solution does not present danger for the human as a user may dip one hand in it without being burned or harmed. The method for removing zinc does not leave any trace of corrosion on the metal and does not cause embrittlement or blistering so that the metal parts may be reused for their original purpose.
It is a first object of this invention to provide a solution for removing zinc coating on the surface of galvanized metal (especially a galvanized steel).
It is another object of this invention to remove zinc coating without affecting the integrity of the metal surface.
It is a further object of this invention to recycle old galvanized metal (especially steel) parts for their original purpose.
It is still a further object of this invention to provide a solution for removing zinc that can be reused many times without hampering its effect.
It is a further object of this invention to provide a safe solution for such a purpose so that humans that manipulate it are not exposed to danger.
It is a further object of this invention to provide a solution allowing to work cold (i.e. at room temperature) to thus save energy.
Still, it is a further object of this invention to provide a solution that allows to recover the zinc in a substantially solid form.